The international mission overseeing the dismantling of Syria's chemical weapons program says it has now been able to verify the non-operation of one of the two remaining sites where safety and security concerns had prevented inspectors from visiting.

The Organization for the Prevention of Chemical Weapons (OPCW) said Thursday the inspection of the site in Aleppo confirmed Syria's declaration that it was dismantled and "long abandoned."

The organization added that the building showed extensive battle damage. Aleppo has been one of the most heavily contested areas of Syria during the country's 32-month crisis.

With the inspection, the joint OPCW-United Nations mission has now verified the location and contents of 22 of Syria's 23 declared chemical weapons sites. Syria has said the last site is also abandoned.

Syria's government has agreed to destroy its chemical weapons by the middle of next year. The OPCW said last week the first phase of the plan, which involved making production equipment inoperable, has been completed.

Syria is now working on providing a detailed plan for how it will destroy its existing chemical weapons stockpile. The OPCW must approve the plan by November 15.